It has been found in practice that there are a number of problems associated with the manufacture, design, installation and use of prior art trench grates for picking up and discharging overland flow of water and other liquids.
Some of the problems with prior art grates include:                (a) During manufacturing, the confined space for welding short lateral bars between two longitudinal flat bars. This process is time-consuming, difficult to clean-up and unattractive. FIG. 1(a) is a plan view of a simple welded prior art grate 100 comprising two longitudinal flat bars 101, a plurality of lateral flat bars 102 joined to the longitudinal flat bars 101 by welds 103. The section view provided in FIG. 1(c) illustrates the confined space available for welding and cleaning-up.        (b) The curved design of some roadways, car parks, kerbing, pathways, etc. requires a curved grate to match both horizontal and vertical curvatures. Existing technology generally forces designers to use short lengths of straight grate to achieve these curvatures, which is not totally satisfactory as this causes noticeable changes of direction and catch points for debris collection. In FIG. 2(a) the gaps between horizontal grate sections are evident and in FIG. 2(b) the vertical change of grade is inconsistent with undulating road and path designs.        (c) A limitation of existing grates is that the lateral bars are generally at right angles to the longitudinal bars 301 and generally vertically oriented as shown in FIGS. 3(a) and (b). This restriction on the design of prior art trench grate installations limits the effectiveness of water entry to the channel below the grate and does not allow effective design to avoid debris pick-up locations.        (d) Contemporary concrete placing machinery used for channels and guttering is often computer-controlled to allow very attractive horizontal and vertical curves. This extends to drainage channels of the kind illustrated in FIG. 4. A short straight grate 402 is difficult to fit into horizontally and vertically curved channels, leaving vertical gaps 403 and horizontal gaps 404 between the grate 402 and the channel 401. This is in addition to the gaps and grade changes shown in FIG. 2.        
Various attempts have been made to overcome the problem of welding in confined spaces noted in (a) above. U.S. Pat. No. 5,024,550 discloses a grate with two longitudinal angle bars with punched holes to reveal L-shaped tabbed ends of lateral flat bars. The space is still somewhat limited on the top end of the tab and the need for slats and tabs is expensive. There is no provision for vertical or horizontal curvature of the grate.
Some attempts have been made to eliminate welding in grates altogether, such as for example in U.S. Pat. No. 4,452,025 where the longitudinal bars have been locked to the lateral bars using rods inserted through the bars at 45° to both bars. This method does not really suit long narrow grates, and it also does not provide any means for horizontal or vertical curvature. Other weld-free grates are disclosed in U.S. Pat. Nos. 5,604,949 and 5,735,008 and these would be more suited to long narrow grates. However they also have no provision for horizontal or vertical curvature.
Some prior art trench grates are designed with a horizontal curvature as shown in FIG. 5. In this type of grate the longitudinal bars are curved and the lateral bars are welded radially from the centre of curvature of the longitudinal bars. However this type of prior art grate cannot easily provide for vertical curvature.
The present invention was developed with a view to providing an improved grate and method of manufacturing a grate that overcomes at least some of the above-noted problems with prior art grates.
References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere.